Add examples for xDS greeter client and server (#26157)

examples/cpp/helloworld/BUILD

@@ -44,6 +44,17 @@ cc_binary(
     ],
 )
 
+cc_binary(
+    name = "xds_greeter_client",
+    srcs = ["xds_greeter_client.cc"],
+    defines = ["BAZEL_BUILD"],
+    deps = [
+        "//:grpc++",
+        "//examples/protos:helloworld_cc_grpc",
+        "@com_google_absl//absl/flags:flag",
+    ],
+)
+
 cc_binary(
     name = "greeter_server",
     srcs = ["greeter_server.cc"],
@@ -64,3 +75,16 @@ cc_binary(
         "//examples/protos:helloworld_cc_grpc",
     ],
 )
+
+cc_binary(
+    name = "xds_greeter_server",
+    srcs = ["xds_greeter_server.cc"],
+    defines = ["BAZEL_BUILD"],
+    deps = [
+        "//:grpc++",
+        "//:grpc++_reflection",
+        "//:grpcpp_admin",
+        "//examples/protos:helloworld_cc_grpc",
+        "@com_google_absl//absl/flags:flag",
+    ],
+)

examples/cpp/helloworld/xds_greeter_client.cc

@@ -0,0 +1,90 @@
+/*
+ *
+ * Copyright 2021 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+#include <iostream>
+#include <memory>
+#include <string>
+
+#include "absl/flags/flag.h"
+
+#include <grpcpp/grpcpp.h>
+
+#ifdef BAZEL_BUILD
+#include "examples/protos/helloworld.grpc.pb.h"
+#else
+#include "helloworld.grpc.pb.h"
+#endif
+
+ABSL_FLAG(std::string, target, "xds:///helloworld:50051", "Target string");
+ABSL_FLAG(bool, secure, true, "Secure mode");
+
+using grpc::Channel;
+using grpc::ClientContext;
+using grpc::Status;
+using helloworld::Greeter;
+using helloworld::HelloReply;
+using helloworld::HelloRequest;
+
+class GreeterClient {
+ public:
+  GreeterClient(std::shared_ptr<Channel> channel)
+      : stub_(Greeter::NewStub(channel)) {}
+
+  // Assembles the client's payload, sends it and presents the response back
+  // from the server.
+  std::string SayHello(const std::string& user) {
+    // Data we are sending to the server.
+    HelloRequest request;
+    request.set_name(user);
+
+    // Container for the data we expect from the server.
+    HelloReply reply;
+
+    // Context for the client. It could be used to convey extra information to
+    // the server and/or tweak certain RPC behaviors.
+    ClientContext context;
+
+    // The actual RPC.
+    Status status = stub_->SayHello(&context, request, &reply);
+
+    // Act upon its status.
+    if (status.ok()) {
+      return reply.message();
+    } else {
+      std::cout << status.error_code() << ": " << status.error_message()
+                << std::endl;
+      return "RPC failed";
+    }
+  }
+
+ private:
+  std::unique_ptr<Greeter::Stub> stub_;
+};
+
+int main(int argc, char** argv) {
+  GreeterClient greeter(grpc::CreateChannel(
+      absl::GetFlag(FLAGS_target), absl::GetFlag(FLAGS_secure)
+                                       ? grpc::experimental::XdsCredentials(
+                                             grpc::InsecureChannelCredentials())
+                                       : grpc::InsecureChannelCredentials()));
+  std::string user("world");
+  std::string reply = greeter.SayHello(user);
+  std::cout << "Greeter received: " << reply << std::endl;
+
+  return 0;
+}

examples/cpp/helloworld/xds_greeter_server.cc

@@ -0,0 +1,106 @@
+/*
+ *
+ * Copyright 2021 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+#include <iostream>
+#include <memory>
+#include <string>
+
+#include "absl/flags/flag.h"
+#include "absl/strings/str_cat.h"
+
+#include <grpcpp/ext/admin_services.h>
+#include <grpcpp/ext/proto_server_reflection_plugin.h>
+#include <grpcpp/grpcpp.h>
+#include <grpcpp/health_check_service_interface.h>
+#include <grpcpp/xds_server_builder.h>
+
+#ifdef BAZEL_BUILD
+#include "examples/protos/helloworld.grpc.pb.h"
+#else
+#include "helloworld.grpc.pb.h"
+#endif
+
+ABSL_FLAG(int32_t, port, 50051, "Server port for service.");
+ABSL_FLAG(int32_t, maintenance_port, 50052,
+          "Server port for maintenance if --secure is used.");
+ABSL_FLAG(bool, secure, true, "Secure mode");
+
+using grpc::Server;
+using grpc::ServerBuilder;
+using grpc::ServerContext;
+using grpc::Status;
+using helloworld::Greeter;
+using helloworld::HelloReply;
+using helloworld::HelloRequest;
+
+// Logic and data behind the server's behavior.
+class GreeterServiceImpl final : public Greeter::Service {
+  Status SayHello(ServerContext* context, const HelloRequest* request,
+                  HelloReply* reply) override {
+    std::string prefix("Hello ");
+    reply->set_message(prefix + request->name());
+    return Status::OK;
+  }
+};
+
+void RunServer() {
+  grpc::EnableDefaultHealthCheckService(true);
+  grpc::reflection::InitProtoReflectionServerBuilderPlugin();
+  int port = absl::GetFlag(FLAGS_port);
+  int maintenance_port = absl::GetFlag(FLAGS_maintenance_port);
+  grpc::experimental::XdsServerBuilder xds_builder;
+  ServerBuilder builder;
+  std::unique_ptr<Server> xds_enabled_server;
+  std::unique_ptr<Server> server;
+  GreeterServiceImpl service;
+  // Register "service" as the instance through which we'll communicate with
+  // clients. In this case it corresponds to an *synchronous* service.
+  xds_builder.RegisterService(&service);
+  if (absl::GetFlag(FLAGS_secure)) {
+    // Listen on the given address with XdsServerCredentials and a fallback of
+    // InsecureServerCredentials
+    xds_builder.AddListeningPort(absl::StrCat("0.0.0.0:", port),
+                                 grpc::experimental::XdsServerCredentials(
+                                     grpc::InsecureServerCredentials()));
+    xds_enabled_server = xds_builder.BuildAndStart();
+    gpr_log(GPR_INFO, "Server starting on 0.0.0.0:%d", port);
+    grpc::AddAdminServices(&builder);
+    // For the maintenance server, do not use any authentication mechanism.
+    builder.AddListeningPort(absl::StrCat("0.0.0.0:", maintenance_port),
+                             grpc::InsecureServerCredentials());
+    server = builder.BuildAndStart();
+    gpr_log(GPR_INFO, "Maintenance server listening on 0.0.0.0:%d",
+            maintenance_port);
+  } else {
+    grpc::AddAdminServices(&xds_builder);
+    // Listen on the given address without any authentication mechanism.
+    builder.AddListeningPort(absl::StrCat("0.0.0.0:", port),
+                             grpc::InsecureServerCredentials());
+    server = xds_builder.BuildAndStart();
+    gpr_log(GPR_INFO, "Server listening on 0.0.0.0:%d", port);
+  }
+
+  // Wait for the server to shutdown. Note that some other thread must be
+  // responsible for shutting down the server for this call to ever return.
+  server->Wait();
+}
+
+int main(int argc, char** argv) {
+  RunServer();
+  return 0;
+}